Vehicles operating in an autonomous mode (e.g., driverless) can relieve occupants, especially the driver, from some driving-related responsibilities. Typically, an autonomous driving vehicle can operate in a complete autonomous mode, a semi-autonomous mode, or a manual mode. When operating in an autonomous mode, the vehicle can navigate to various locations using onboard sensors, allowing the vehicle to travel with minimal human interaction or in some cases without any passengers. When operating in a semi-autonomous mode, a driver of the vehicle can take over the driver at certain points while the vehicle can operate autonomously in other time. When operating in a manual mode, the driver take full control of the vehicle in all time.
One of the important features of autonomous driving is a lane assistant system or lane departure warning or assistant system. A lane assistant system is a mechanism designed to warn or assist the driver when the vehicle begins to move out of its lane on freeways and arterial roads, especially when the vehicle is operating in a semi-autonomous mode. These systems are designed to minimize accidents by addressing the main causes of collisions: driver error, distractions and drowsiness. Typical lane assistance is provided based on the relative moving direction of a vehicle with respect to the line marking painted on the lane to determine whether a vehicle is drifting out of the current lane. However, such a determination does not always accurately catch driver's intention (e.g., whether the driver indeed wants to change lane or exit the lane). If the lane assistant system attempts to automatically correct the vehicle moving direction against the driver's actual intention, it may cause an uncomfortable or unsafe situation.